The disclosure generally relates to a real time clock device and, more particularly, to the signal generating circuit for the real time clock device.
The real time clock device may be used to generate a signal indicating the current time (referred to as “the real time signal” hereinafter for conciseness). The real time clock devices possess the advantage of low power consumption and therefore are widely utilized in computers, cameras, mobile phones, and other electronic devices.
The real time clock device relies on a signal generating circuit and a signal processing circuit for generating the real time signal. For example, the signal generating circuit may generate a 32.768 KHz oscillating signal as a clock signal. The signal processing circuit may generate the real time signal according to the 32.768 KHz oscillating signal. The signal processing circuit may also generate a power on reset (POR) signal for resetting the circuit elements in the real time clock device after the power is normally supplied so that the real time clock device may operate correctly.
As the trends of energy conservation and environmental protection become prominent, many electronic devices are required to consume less and less power. The real time clock device, which continuously operates to generate the real time signal, must therefore improve the energy consumption efficiency. For example, some signal generating circuit operates with lower voltages or currents to conserve power. The signal generating circuit operating under lower voltages or currents usually suffers from the longer startup time and the instability caused by the noises, and therefore generates erroneous clock signals. The real time clock device may not generate the correct real time signal and may not even function at all.
Moreover, the signal generating circuit operating with lower voltages or currents may often need to be restarted because of the instability caused by the noises. When a simple resistor-capacitor circuit is used to generate the POR signal, the circuit may not generate the POR signal in suitable time because of the frequently occurred restarts. The circuit elements in the real time clock device may not be reset appropriately and therefor the real time clock device may not function correctly.